1. Field of the Invention
The present invention relates in general to a bar-type slide guiding apparatus for use in, for example, machine tools. More particularly, it relates to an apparatus for slidably guiding a slide member by means of hydrostatic bearings along a pair of pilot bars.
2. Description of the Prior Art
In a known side guiding apparatus of this knds, a slide member is slidably guided along a pair of pilot bars fixedly supported on a guide base in parallel relation. Hydrostatic air bearings through which a pair of pilot bars pass are respectively mounted in two or more guiding portions thereof and enable the slide member to slide precisely and smoothly. However, the known apparatus requires that the clearance between the external surface of each pilot bar and the internal surface of an associated bearing be precisely maintained constant. In other words, each of the bearings has such a construction as to forcibly align the axis of its internal surface with the axis of each pilot bar associated therewith. Accordingly, when errors in machining and assembling and thermal deformation cause the pair of pilot bars to lose the parallelism therebetween and to tilt relative to each other, the clearance between the internal surface of each bearing and the external surface of each pilot bar associated therewith is varied as the slide member moves. This disadvantageously results in deforming each pilot bar and deteriorating the guiding accuracy. Moreover, an excessive variation of such clearance brings about the contact of each bearing with the associated pilot bar, thereby effecting the dead locking of the slide member on the pilot bars.
Generally, each of such bearings is fitted in a cylindrical bore formed in the guiding portion of the slide member and is secured thereto by fixing a flange portion of the bearing on the slide member by means of bolts. The difference between the bearings and the slide member in material causes the difference therebetween in thermal expansion. This brings about a loosening between the external surface of each bearing and the internal surface of the associated guiding portion, whereby a misalignment takes place between the axes of each bearing and the associated pilot bar.